1. Field of the Invention
The present invention relates to aqueous solutions or dispersions of cross-linkable, cationic polyurethanes having reversibly blocked amino groups incorporated via urethane groups which may react with blocked isocyanate groups in the heat, to a process for the production of these solutions or dispersions and to the use thereof for the production of coatings on heat-resistant substrates and in particular on metals by cathodic separation.
2. Description of the Prior Art
Reaction constituents having reversibly blocked amino groups for organic polyisocyanates having optionally blocked isocyanate groups are already known. DE-AS No. 1,520,139, for example, describes heat cross-linkable two-component systems which harden to produce polyureas, in which one component contains free isocyanate groups and the other component contains reversibly blocked amino groups in the form of aldimine or ketimine groups. DE-AS No. 1,694,237 describes heat cross-linkable combinations of NCO-prepolymers having phenol-blocked isocyanate groups and aliphatic or aromatic compounds having ketamine and/or enamine groups.
It has now surprisingly been found that certain tert. amines (which are produced by the Michael addition of secondary amines to specific acrylic acid derivatives) are, on the one hand, masked secondary amines which do not react at room temperature with polyisocyanates having blocked isocyanate groups and react with them at a moderately elevated temperature of about 90.degree. to 130.degree. C. with the production of urea. On the other hand they may be converted into quaternary and more particularly ternary ammonium groups using quaternizing agents and particularly organic or inorganic acids. The oligourethanes having masked isocyanate groups and quaternary and more particularly ternary ammonium groups of the above type represent self cross-linkable binders which may be dissolved or dispersed in water for coating agents which are processed from the aqueous phase and may be particularly applied to metallic substrates by cathodic deposition. Oligourethanes having quaternary and more particularly ternary ammonium groups of the above type represent cross-linkable binders when combined with blocked polyisocyanates. Such combinations may also be dissolved or dispersed in water for coating agents which are processed from the aqueous phase.